The term encapsulation refers to the formation of a matrix surrounding a solid, liquid, or gaseous material. The encapsulation process is often used to turn sensitive, reactive, or unstable substances into protected and easily administered compounds. In the food and pharmaceutical industries, encapsulation of food ingredients is used for a number of applications including coating, smell or taste masking, increasing shelf life, improved processing, protecting sensitive materials, and delivering specific doses. Coacervation is the most commonly used method of encapsulation due to its high encapsulation yield and its controlled release capability. In general, coacervation refers to the formation of phase separated aggregates and the subsequent adsorption of the aggregates around a core material. Coacervation may be either complex (i.e. using two oppositely charged polyelectrolytes) or simple (i.e. using a single polyelectrolyte).
The most extensively used positive polyelectrolyte in coacervation is gelatin, a protein derived from collagen. The most often used negatively-charged polyelectrolyte in combination with gelatin is gum arabic, a polysaccharide exuded from acacia trees. Complex coacervation of gelatin and gum arabic has been widely used because both compounds are non-toxic, natural, and biodegradable.
Generally, current state-of-the-art coacervation processes using gelatin and gum arabic include the following four steps: emulsification, coacervation, wall formation, and wall hardening. Typically, the process begins by mixing gelatin and the gum arabic, and adjusting the pH of the mixture. The core material is then emulsified in the mixture, followed by another pH adjustment which causes the gelatin and gum arabic to coacervate. The coacervate mixture is then cooled to induce wall formation of the microcapsules. Finally, a hardening or a crosslinking agent such as glutaraldehyde is added to the microcapsules to harden the capsules wall.
There are several disadvantages associated with current coacervation processes. For example, gelatin-gum arabic coacervation requires several pH adjustment and dehydration steps. Furthermore, a toxic crosslinking agent such as glutaraldehyde or formaldehyde is usually needed to complete hardening of the microcapsule walls. Such toxic compounds are undesirable for use in the food industry.
Consequently, there is a need for a simple encapsulation method without the use of toxic compounds.